Underground pipes and extensive underground pipeline systems have been in existence for many, many years. For a number of years, many of the underground pipe and pipeline systems have been built using plastic or polymer pipe, constructed of polymeric materials of all kinds, including polypropylene (PP), polyethylene (PE), high-density polypropylene (HDPP), high-density polyethylene (HDPE) and polyvinyl chloride (PVC), by way of example. The type of material depends upon the function and requirements of a pipeline, whether for drainage or pumping of water, sewage, gas, oil, liquid chemicals and even slurries of solid materials mixed in a fluid carrier for transport through the pipeline. These underground pipes, although highly durable, may need to be replaced, for many reasons. For example, the existing pipeline may be in poor condition due to chemical or biological degradation, wear, corrosion, ground-shifting or other destructive modalities. Modified usage requirements may require a larger pipe or might require pipe constructed of a different material, such as a particular chemically-compatible material.
The usual means for replacing pipelines has been to excavate entirely along the length of pipeline or along the section of pipeline to be replaced, remove it and replace it with appropriate, new pipe. This process is costly, labor-intensive, uses large quantities of fuels to power the construction equipment and often adversely impacts the above-ground environment, including disruption to vehicular traffic, interruption of natural wildlife habitats and has the potential of acceleration of erosion.
In the case of replacement of brittle or fracturable cast-iron water or gas mains, prior apparatuses and methods have been proposed, such as those disclosed in U.S. Pat. Nos. 4,505,302; 4,720,211; and 4,738,565, all of which were originally assigned to British Gas Corporation of England in patents issued Mar. 19, 1985, Jan. 19, 1988 and Apr. 19, 1988, respectively. These prior devices included an elongated pipe-fracturing and displacement mole having a rear cylindrical body portion and a conical front pipe-fracturing and expanding portion. Specifically, the front portion includes a fracturing means for applying an intense localized pressure outwardly against the inside of the buried pipe. The mole was forced through the existing pipeline employing a plurality of high-tensile strength cutters in the shape of tapered chisel edges formed with two elongated faces intersecting at an obtuse angle and which elongated edges are at a shallow angle relative to the axis of the mole or the pipeline to be replaced. The cutter edges expand from a small diameter shallow angle at the front of the mole to a larger diameter at the cone portion. The largest diameter defined by the cutter edges is sufficiently large to fracture the pipe but is no larger than the largest diameter of the expanding cone which is positioned immediately behind the rearward extent of the tapered edges. The devices are specifically designed for applying high, localized fracturing force to fracturable pipes.
Applicant has found that the high localized force exerting devices of the '302, '211, '565 patents do not cause fracturing of polymeric pipes of the type which are to be replaced according to the present invention. Such devices, particularly devices having cutting edges formed with elongated intersecting flat faces at an obtuse angle are not sufficiently sharp to pierce some of the polymeric pipe materials used. Fracturing is not likely to result even with some of the most rigid polymeric pipe materials, such as PVC. Polymeric pipe has not been found to be fracturable as with cast iron gas pipes and water mains for which prior devices were useful.
Other devices have previously been proposed for use in splitting or piercing metallic well casings, as in U.S. Pat. Nos. 652,367; 1,001,205; 1,519,882; 1,618,368; 2,638,165; and 2,947,253. Still other devices have been proposed for splitting and removing metallic tubing of the type sometimes used in heat exchangers, such as those depicted in U.S. Pat. Nos. 2,834,106 and 2,983,042. All of these devices use one or a plurality of cutting edges, acting outwardly against the pipe as the device is moved through the pipe. Each cutting edge, whether a fixed or movable blade, or a circular roller blade has an outwardly tapered edge tilted or angled back from the nose of the device. These devices are considered to be inadequate for splitting and replacement of polymeric pipe. A single blade cutting longitudinally along a polymeric pipe allows the resilient material to return to its circular "C" shape after the blade passes through it. The single-cut resilient pipe cannot be expanded adequately to draw a replacement pipe into it. The body of the tool and the replacement pipe are "gripped" by the collapsing "C" of the cut polymeric pipe, even using an expanding mandrel. In situations where a plurality of radially projecting blades is used, each blade angled back to present a progressively larger diameter cutting edge, it has been found that only one of the plurality of outwardly projecting back-angled blades would pierce the pipe wall. The other blades merely ride along the inside of the pipe. The first cut allows the polymeric pipe to be temporarily expanded outwardly as the other blades pass through it, and the resilient hoop tension collapses the pipe toward its prior diameter. Thus, a polymeric pipeline could not be consistently cut into a plurality of strips and could not be consistently properly expanded to allow efficient and smooth insertion of a new replacement pipe of the same or larger size or diameter.
Other devices for drawing a replacement pipe or tubing or a supplemental pipe, tubing or lining into an underground pipeline, either by expanding the ground, expanding the existing pipe or simply drawing in a smaller diameter pipe, are shown in U.S. Pat. Nos. 4,100,980; 3,181,302 and 4,003,122. None of these devices adequately address the problems associated with splitting and replacing a polymeric pipe.
Some devices were proposed for cleaning contaminates from boiler tubing or from flues by cutting out the contaminates as in U.S. Pat. Nos. 928,361 and 2,163,384, but these did not address splitting, expanding and removing such pipes. One device proposed a plurality longitudinally aligned "saw tooth" blades, each progressively cutting deeper into the pipeline wall from the inside. The wall was sufficiently weakened, without cutting entirely through it, so that its outward tension was relaxed, and removal was facilitated.